1. Field of the Invention
This invention relates to lens drive devices and more particularly to a device for driving zoom lens and focusing lens by a motor.
2. Description of the Related Art
There have been previous proposals for driving an optical element, for example, a focusing lens in a lens barrel by a motor, as, for example, disclosed in U.S. Pat. No. 4,152,060 and Japanese Laid-Open Patent Application Nos. Sho 56-147132, Sho 57-20710, Sho 59-116627 and Sho 59-116628 . The motor shown in the above-cited documents has as its constituent parts a rotor and stator formed in a hollow shape. The hollow stator provides a space through which light coming from an object can be photographed or provides a space housing a lens system.
By the way, the lens barrels, particularly zoom lens barrels, have two lens systems, namely, a zoom lens system movable for zooming, and a focusing lens system movable for focusing. Accordingly, when the zooming and the focusing are motorized, it is required to use two independent motors. If it is desired to arrange these two motors in a lens barrel, the complexity of the structure and the size of the lens mounting mechanism are increased.
In the field of motors, a so-called double cup type motor has been proposed in Japanese Laid-Open Patent Application No. Sho 59-175368. The motor of this type includes a frame, a field magnet of a first motor arranged on the inside of the frame, a cup-shaped rotor of the first motor arranged in the field magnet with a gap held therebetween, a fixed iron core of the first motor arranged in the cup-shaped rotor with an air gap therebetween, a field magnet of a second motor arranged inside of the fixed core of the first motor through an intermediary of non-magnetic material, a second cup-shaped rotor arranged with a gap from the field magnet, and a fixed iron core of the second motor arranged inside of the cup-shaped rotor with an air gap therebetween, wherein the aforesaid first and second cup-shaped rotors are fixedly secured to first and second output shafts respectively, and the first and second output shafts are arranged on a common axis to the left and right of the frame.